Science —

Evolution

Evolution is a change in the frequency of specific forms (alleles) of genes …

On the simplest level, evolution is a change in the frequency of specific forms (alleles) of genes over time. These changes can come about through selection or genetic drift, and they change the properties of the population. If the changes come about through a selective pressure, they will generally help organisms within the population to adapt to their environment or outcompete their peers for the production of offspring.

Over time, these changes can accumulate, and produce populations that are visibly or biochemically distinct. These differences can ultimately produce reproductive isolation, either through hybrid infertility (i.e., donkeys and horses) or through differences in habitat and behavior (i.e., brown and polar bears). This process ultimately produces new species. Reproductive isolation as the product of environmental selection has been observed in the lab.

In addition to the biological process of evolution, the term is also used to refer to the history of life on Earth, since fossil evidence clearly indicates that many evolutionary transitions occurred following the origina of multicellular life. Examples of well-documented transitions include the origin of humans, whales, horses, birds, and mammals.